Fixing SPDX Expression Warning in package.json

If you ever run into the following warning when installing your NPM package:

npm WARN package.json rookeries-api-client-wrapper@0.4.9 license should be a valid SPDX license expression

That means you have an improper a name for the specified license in your package.json. So what are valid values for licenses? Well… here is the SPDX list of licenses